1. Field of the Invention
The invention relates to film cassettes or cartridge leaders for microfilm and particularly to a means whereby the leader strip that projects from the throat on the cassette can be pulled out the proper distance to cause it to self-thread automatically into a microfilm reader or printer.
2. Description of the Prior Art
It is common practice to provide cartridges, cassettes or magazines which contain a roll of microfilm, the most common being 16 mm., wherein the cassette is placed in a reader or reader-printer and the leader strip is supposed to be picked up by the mechanism of the machine and automatically moved into position whereby the frames on the film can be separately viewed by moving the film through the machine.
One of the problems has been that the end of the film is not properly positioned to be engaged by the mechanism of the machine to cause the film to be automatically threaded.
Various types of leaders have been proposed, such as that of U.S. Pat. No. 3,655,145, where the leader has a widened portion to prevent it from disappearing into the cartridge when the film is rewound and an open window to enable it to be picked up.
Some of them use spade-shaped ends for the same purpose, such as shown in U.S. Pat. No. 3,379,387.
More recently it has become the practice to provide a leader, the same width as the film with a plastic button inserted through the film leader, near the end, to provide a plug or slug integral with the film which projects from each side thereof that prevents the film from being entirely retracted into the housing and can also be used to engage with the reader leader pickup mechanism to draw the film into and automatically thread it into the reader or reader-printer. Thus the film may be rewound until the button engages with the throat of the film container and does not project beyond the guide to the throat enabling the cassette to be more conveniently stored in a suitable file.
When it is desired to use the film, the end of the leader at the button is pulled outward a certain distance and then the cassette placed in a receptacle on the reader or reader-printer where it is picked up by the mechanism of the machine.
The problem has been to pull the leader out to exactly the right distance to enable it to be picked up.